1. Field of the Invention
The present invention relates to a liquid metal ion source (LMIS), and more particularly to an art of making the ion emission of a Ga liquid metal ion source stable and long life time.
2. Description of the Prior Art
A liquid metal ion gun includes a vacuum chamber in which a liquid metal ion source is set, and the liquid metal ion source electrically insulated from the vacuum chamber. A high voltage cable capable of supplying current between both terminals of the liquid metal ion source is connected to the liquid metal ion gun and thereby, it is possible to supply a high voltage to the liquid metal ion source so as to apply the high voltage to the liquid metal ion source appropriately and to heat the liquid metal ion source by turning on electricity.
It is possible to adjust an ion emission quantity (emission current) by voltage between the liquid metal ion source and an extract electrode. The emitted ions are received by a beam limiting aperture (gun aperture).
It is important to stably maintain the ion emission of the above Ga liquid metal ion source. However, in order to do so, it is necessary to stably supply gallium (hereafter referred to as “Ga”) consumed by the ion emission, from a reservoir. A condition in which the emission current is stable is a condition in which consumption of Ga is balanced with supply of Ga, that is, a balance equilibrium eutectic condition in which Ga is supplied by an amount as consumed for the ion emission.
However, if a foreign material is mixed into Ga, the supply of Ga may be interrupted, and if the purity of Ga is changed, physical properties are changed to lose the balance between the consumption and the supply of Ga. Accordingly, the stability of emission becomes deteriorated.
In order to obtain stable emission, it has been constructed conventionally such that an emission ion beam is hot directly irradiated onto an extractor electrode so as not to admix a foreign material into Ga. Further, an electrode (beam limiting aperture) receiving emission of a beam is constituted by a chemical compound metal of Ga which does not interrupt supply of Ga even if Ga is subjected to a buildup of a contaminating material due to adhesion of back-sputtered particles of the electrode receiving emission of the emission ion beam to Ga, that is, a metal (Sn or In) not raising the melting point of Ga.
Furthermore, because the number of back-sputtered particles (or particles causing contamination) to be re-adsorbed to LMIS is decreased proportionally to the square of the distance between the emitter and the beam limiting aperture, the distance between the emitter and the beam limiting (GUN) aperture has been separated.
For example, Japanese Patent Publication No. 3190395 discloses a technique for constituting a portion irradiated with an ion beam by a sintered body in which a low-melting-point metal is infiltrated. JP-A-2001-160369 discloses a technique for, when using common Ga as a liquid metal ion source, using the same kind of Ga as a restricting material for protection. In addition, JP-A-4-14455 discloses that a surface of an emitter electrode or the emitter electrode is constituted by one or more of melted metals set to a tip end of the emitter electrode or metals constituting an alloy.